Process for making air gap containing semiconducting devices and resulting semiconducting device

ABSTRACT

A method of forming at least a partial air gap within a semiconducting device and the resulting devices, said method comprising the steps of: (a) depositing a sacrificial polymeric composition in one or more layers of the device during its formation; (b) coating the device with one or more layers of a relatively non-porous, organic, polymeric, insulating dielectric material (hardmask) having a density less than 2.2 g/cm 3 ; and (c) decomposing the sacrificial polymeric composition such that the decomposition products permeate at least partially through the one or more hardmask layers, thereby forming at least a partial air gap within the device.

The invention herein described relates generally to the fabrication ofsemiconducting devices and more specifically to such devices that useair gaps to reduce capacitive coupling between conductors in suchdevices. Examples of semiconducting devices include the well knownintegrated circuits (ICs) as well as routers and switches forcontrolling electrical or optical signals.

As a consequence of the progress made in integrated circuit technology,the spacing between the metal lines on any given plane of an integratedcircuit has become less and less, now extending into the submicrometerrange. By reducing the spacing between conductive members in theintegrated circuit, an increase in capacitive coupling occurs. Thisincrease in capacitive coupling causes greater crosstalk, highercapacitive losses and increased RC time constant.

In order to reduce capacitive coupling, much effort has been directedtoward developing low dielectric constant (low-K) materials to replaceconventional dielectric materials that are interposed between the metallines on a given layer and between layers. Many conventional electronicinsulators have dielectric constants in the 3.5 to 4.2 range. Forexample, silicon dioxide has a dielectric constant of 4.2 and polyimidestypically have dielectric constants from 2.9 to 3.5. Some advancedpolymers have dielectric constants in the 2.5 to 3.0 range. Materials inthe 1.8 to 2.5 range are also known.

The lowest possible, or ideal, dielectric constant is 1.0, which is thedielectric constant of a vacuum. Dehumidified air is almost as good witha dielectric constant of 1.001. With this recognition of the lowdielectric constant of air, attempts have been made to fabricatesemiconductor devices with air gaps between metal leads to reduce thecapacitive coupling between the electrically conducting members. The airgap forming techniques that have been developed have varying degrees ofcomplexity and include subtractive and damascene techniques.

U.S. Pat. No. 4,987,101 describes a method and structure for providingan insulating electrical space between two lines on a layer of materialor between lines on adjacent layers of material. A base member is formedhaving a plurality of support members extending outwardly from the basemember. A removable material is deposited on the base member and aroundthe support members. A cap member of insulating material is thendeposited over said support members and the removable material. Accessopenings are formed in at least one of the base member or the cap membercommunicating with the removable material. The removable material isremoved through the access openings to thereby define a space betweenthe cap member and the base member and between the support members.During this step a partial vacuum (in which some inert gas may bedispersed) may be created in the space vacated by the removablematerial. The access openings are then filled in so as to provide asealed space between the cap member which has a very low dielectricconstant.

U.S. Pat. No. 5,324,683 describes several techniques for forming airgaps or regions in a semiconductor device. The air regions are formed byeither selectively removing a sacrificial spacer or by selectivelyremoving a sacrificial layer. The air regions are sealed, enclosed orisolated by either a selective growth process or by a non-conformaldeposition technique. The air regions may be formed under any pressure,gas concentration or processing condition.

The techniques disclosed in the aforesaid patents rely on holes or otherpassageways for effecting removal of the sacrificial material. In U.S.Pat. No. 5,461,003, a sacrificial material is removed through a porousdielectric layer. According to this patent, metal leads are formed on asubstrate, after which a disposable solid layer is deposited on themetal leads and substrate. The disposable solid layer is then etchedback to expose the tops of the metal leads. Then a porous dielectriclayer is deposited over the metal leads and disposable layer. This isfollowed by removal of the disposable layer which is said to bepreferably accomplished by exposing the device to oxygen oroxygen-plasma at a high temperature (greater than 100 degrees Celsius)to vaporize, or burn off, the disposable layer. The oxygen moves throughthe porous dielectric layer to reach and react with the disposable layerand thereby convert it to a gas that moves back out of the porousdielectric layer. Upon removal of the disposable layer, air gaps areleft. Finally, a non-porous dielectric layer is deposited on top of theporous dielectric layer to seal the porous dielectric layer frommoisture, provide improved structural support and thermal conductivity,and passivate the porous dielectric layer. This procedure results in anair gap that does not extend the full height of the adjacent metal leadsor lines. The '003 patent discloses a modified method to remedy thisproblem and to increase the process margin. This modified methodinvolves a further process step wherein an oxide layer is formed on topof the metal leads so that the disposable dielectric layer can extendhigher than the metal leads.

In U.S. Pat. No. 6,165,890 a sacrificial norbornene polymer is usedbetween the metal lines of a semiconductor device and then the device isheated to decompose said polymer leaving an air gap between said metallines. The decomposition products may be removed through holes orpassages in the dielectric layer (col. 17, line 12), but preferably theyare allowed to diffuse through a solid, porous, inorganic, permanentlayer. One suitable dielectric layer comprises a silica-based xerogelcontaining from 10 to 90 percent porosity. In U.S. Pat. No. 6,451,712, aporous dielectric material is formed by decomposition of porogenscontained in a thermoplastic matrix and permeation of the decompositionproducts of such pore forming materials through a hard mask.

Kohl, et al., IEEE Electron Device Letters, Vol. 21, No. 12, December2000, p557-559 teach that critical material properties of a sacrificialpolymer include: (a) a glass transition temperature sufficiently high toprovide dimensional stability during processing (for example, greaterthan 350 degrees Celsius); (b) a sufficiently slow decomposition rate tomitigate problems of pressure build-up during air gap formation; (c) noobjectionable residue after decomposition; and (d) a temperature ofdecomposition sufficiently low (for example, 450 degrees Celsius) tomitigate device damage that may occur at higher temperatures. Additionalrequirements for such decomposable sacrificial polymers are disclosed inIBM Technical Disclosure Bulletin, Vol. 38, No. 9 September 1995,p137-140.

According to the present invention there is provided a method of formingat least a partial air gap within a semiconducting device comprising thesteps of: (a) depositing a sacrificial polymeric composition in one ormore layers of the device during its formation; (b) coating the devicewith one or more layers of a relatively non-porous, organic, polymeric,insulating dielectric material (hardmask) having a density less than2.2, preferably less than 2.0, more preferably less than 1.5, and mostpreferably less than 1.3 g/cm³; and (c) decomposing the sacrificialpolymeric composition such that the decomposition products permeate atleast partially through the one or more hardmask layers, thereby formingat least a partial air gap within the device.

In addition, the present invention provides a semiconductor device,especially such a device prepared according to the foregoing method,comprising a substrate layer, one or more conductive layers, at leastone layer of a relatively non-porous, organic polymeric insulatingdielectric material (hardmask) having a density less than 2.2,preferably less than 2.0, more preferably less than 1.5, and mostpreferably less than 1.3 g/cm³, and optionally an impermeable organic orinorganic sealing layer, wherein at least some portion of the conductivelayer is separated from another portion thereof by at least a partialair gap.

The use of a hardmask composition in a coating layer over a sacrificialpolymer layer would normally be expected to result in blistering ordelamination as sacrificial polymer layer is decomposed unless chimneysor pores are introduced into the hardmask layer to assist in removal ofvolatile decomposition products of the sacrificial polymer.Surprisingly, the present inventors have discovered that such blisteringor delamination can be avoided if an organic hardmask layer having adensity less than 2.2, preferably less than 2.0, more preferably lessthan 1.5, and most preferably less than 1.3 g/cm³ is employed.

In a separate embodiment of the invention, the permeability of thehardmask is further improved by subsequently introducing porositytherein, thereby further reducing the density of the hardmask layer.According to this embodiment of the invention, prior to orsimultaneously with step (c), the one or more layers of an insulatingdielectric material are treated so as to reduce the density and/orincrease the permeability thereof to decomposition products of saidsacrificial polymeric composition.

FIGS. 1-6 are diagrammatic cross-sections of a portion of asemiconductor structure, illustrating several steps of the presentmethod.

For purposes of United States patent practice, the contents of anypatent, patent application, provisional patent application, orpublication referenced herein is hereby incorporated by reference in itsentirety herein, especially with respect to its disclosure of monomer,oligomer, polymer, or semiconductor structures, synthetic ormanufacturing techniques and general knowledge in the art. If appearingherein, the term “comprising” and derivatives thereof is not intended toexclude the presence of any additional component, step or procedure,whether or not the same is disclosed herein. In order to avoid anydoubt, all compositions claimed herein through use of the term“comprising” may include any additional additive, adjuvant, or compound,unless stated to the contrary. In contrast, the term, “consistingessentially of” if appearing herein, excludes from the scope of anysucceeding recitation any other component, step or procedure, exceptingthose that are not essential to operability. The term “consisting of”,if used, excludes any component, step or procedure not specificallydelineated or listed. The term “or”, unless stated otherwise, refers tothe listed members individually as well as in any combination.

The term “partially” or “at least partially” refers to the possibilitythat some portion of the sacrificial polymeric material or a degradationproduct residue thereof may remain in the semiconductor structureaccording to the present invention. Desirably at least 90 percent byweight, more preferably at least 99 percent by weight of the sacrificialpolymer is lost and replaced by air or an inert gas in the resulting airgap. Additionally, at least 50 percent, more preferably at least 90percent by weight of the decomposition products are removed by means ofpermeation through the hardmask layer or layers according to theinvented process, any remainder exiting the structure between conductorlayers or by voids or holes therein, or by other means.

By the term “relatively nonporous” is meant that the amount of pores inthe hardmask are insufficient to permit escape of volatile decompositionproducts. Preferably 50 percent or less and more preferably at least 10percent or less of such volatile decomposition products are removed fromthe resulting structure by means of voids or pores in directcommunication with the outside of the structure.

By the term “decomposition” or “decomposition products” is meantproducts of lower molecular weight formed upon depolymerization ordegradation of the sacrificial polymer or the composition comprising thesacrificial polymer layer. Such products may be formed by purely thermaldepolymerization or degradation (volatilization) or through the actionof a chemical agent such as oxygen, ozone, or fluorine.

Suitable sacrificial compositions for use in the present method includeorganic and inorganic polymeric materials that are subject todecomposition upon heating, optionally in the presence of a chemicalagent. Examples of inorganic materials include solid inorganics, such asfluorinated amorphous carbon, as well as sulfide, oxide, carbide, andcarbonate materials that are subject to thermal decomposition. Examplesof organic materials include carbon, silicon or sulfur containingpolymers containing at least some C—C bonds, that are similarly subjectto thermal decomposition. Preferred sacrificial compositions are organicpolymers, especially polyamides, polyacrylate-, polyvinylaromatic-,benzocyclobutene-, and polycycloolefmic-polymers.

Preferred sacrificial polymers include homopolymers and copolymerscomprising polymerized reaction products of acrylate-, methacrylate-,vinylaromatic-, norbomene-, vinylbenzocyclobutene-, or ethynylarylsubstituted 1,3-cyclopentadienone-monomers. Preferred copolymers includethe foregoing monomers that are copolymerized with one or morepolymerizable comonomers. Highly preferred polymers are the well knownbisbiscycloolefins, especially homopolymers and copolymers based onnorbornenes or substituted norbomenes.

Additional examples include copolymers of a first monomer selected fromacrylates, vinylaromatics, norbomenes, and alkyldiol diacrylates with asecond monomer selected from vinylbenzocyclobutenes or 1,3 bis2[4-benzocyclobutenyl (ethenyl)]benzene. Highly desirably, thesacrificial polymer comprises a sufficient quantity of the firstmonomer, preferably from 99 to 40, more preferably from 95 to 75 molepercent, based on total monomer content of the polymer, and selected togive the polymer the desired decomposition temperature and a sufficientquantity of the second monomer, preferably from 1 to 60, more preferablyfrom 5 to 25 mole percent, based on total monomer content of the polymerselected to give the polymer the desired glass transition temperature.Using this approach, it is possible to obtain a polymer having adecomposition and glass transition temperature tailored to the specifictemperature requirements for processing air gap semiconductorstructures.

Specific examples of suitable copolymers include copolymers of (a)5-ethylidene-2-norbomene and vinylbenzocyclobutene (or avinylbenzocyclobutene derivative); (b) 5-ethylidene-2-norbornene and5-(3-benzocyclobutylidene)-2-norbornene; (c) styrene (or a styrenederivative) and 5-3-benzocyclobutylidene)-2-norbomene; (d) styrene (or aderivative of styrene) and vinylbenzocyclobutene (or avinylbenzocyclobutene derivative); and (e)bis[3-(4-benzocyclobutenyl)]1,n (n=2-12)alkyldiol diacrylate and 1,3 bis2[4-benzocyclobutenyl (ethenyl)]benzene.

The term “derivative of styrene” used herein means Ar—CR═CH, wherein Ris an alkyl group containing from 1-6 carbon atoms which may be mono ormultisubstituted with functional groups such as nitro, amino, cyano,carbonyl and carboxyl and wherein Ar is phenyl, alkylphenyl, naphthyl,pyridinyl or anthracenyl.

The term “vinybenzocyclobutene” means bicyclo[4.2.0]octa-1,3,5-triene,2-ethenyl and bicyclo[4.2.0]octa-1,3,5-triene, 3-ethenyl, i.e, theethylene group is attached to the benzene ring and not the cyclobutenering.

The term “derivative of vinylbenzocyclobutene” means that one or more ofthe hydrogens of vinylbenzocyclobutene are replaced with an alkyl, aryl,alkylaryl or hetero atom group(s) which may be mono or multisubstitutedwith functional groups such as nitro, amino, cyano, carbonyl andcarboxyl.

The substrates used in this invention may be any substrate on whichthere is a desire to form a patterned, conductive layer. Typically, suchsubstrate will include silicon wafers with or without lower level metalinterconnect structures formed thereon.

Suitable sacrificial polymers for use herein include organic polymers(that is polymer comprising at least some carbon atoms and optionallyheteroatoms such as oxygen or silicon in the backbone) or inorganic(that is lacking carbon atoms in the backbone, and preferably consistingof silicon, boron and other metal or metalloid atoms and, optionallyoxygen atoms in the backbone). Examples of suitable organic polymersinclude polyvinylaromatic polymers such as polystyrene,poly-α-methylstyrene, copolymers of a vinylaromatic polymer and acomonomer; polyacrylonitriles, polyethylene oxides, polypropyleneoxides, polyethylenes, polylactic acids, polysiloxanes,polycaprolactones, polyurethanes, polymethacrylates, polyacrylates,polybutadienes, polyisoprenes, polyamides, polytetrahydrofurans,polyvinyl chlorides, polyacetals, amine-capped alkylene oxides,polylactides, polylactates, polypropyleneoxides, and ethyleneglycol/poly(caprolactones). Examples of inorganic polymers within theabove definition are silica, siliconcarbide, and silsesquioxanes lackingcarbon in the polymer matrix.

Preferred examples of organic polymers are polyarylenes, includingpolyarylene ethers (for example SiLK™ dielectric resins from The DowChemical Company, Flare™ resins from Honeywell), polyorganosiloxanes,and benzocyclobutene based resins (for example Cyclotene™ resins fromThe Dow Chemical Company). Additional suitable organic polymers usefulas sacrificial polymers are the reaction product of monomers comprisingcyclopentadienone functional groups and acetylene, preferablyphenylacetylene, functional groups. Examples include polymers disclosedin U.S. 5,965,679, and in copending U.S. patent application Ser. No.10/078205, filed Feb. 15, 2002.

A most preferred organic polymer for use as a sacrificial polymer is acopolymer of one or more vinylaromatic monomers, especially styrene, andone or more vinylbenzocyclobutene comonomers, containing from 50 to 90mole percent, preferably from 60 to 80 mole percent polymerizedvinylaromatic monomer. Such polymers are readily prepared bycopolymerization of vinyl functionality of the separate monomers withresultant crosslinking occurring in the polymer due to residual ringopening of cyclobutene functionality at elevated processing temperaturesduring application and curing of the hardmask layer.

The sacrificial polymer may include one or more poragens which areoccluded polymers of a different composition or form that are designedto readily decompose and leave a more porous structure with greater gaspermeability within the sacrificial polymer layer. The porogen, or poreforming material can also enable the sacrificial polymer to decompose instages without detrimental rapid gas evolution which can lead toblistering or delamination of the semiconductor layers or the hard maskitself.

Suitable poragen materials include linear, branched, star,hyperbranched, dendritic, and cross-linked oligomers or polymers. Onepreferred porogen morphology is cross-linked polymeric nanoparticles.The porogen, optionally, is chemically bonded to a matrix material, forexample by inclusion of a reactive functionality which will bond to thematrix. Suitable chemistries for the porogen depend in part upon thematrix material selected. Preferably, the sacrificial polymer includingany porogen decompose at temperatures in the range of about 250 to about400° C. Suitable poragen polymers include polyvinylaromatic polymerssuch as polystyrene and poly-α-methylstyrene; polyacrylonitriles,polyethylene oxides, polypropylene oxides, polyethylenes, polylacticacids, polysiloxanes, polycaprolactones, polyurethanes,polymethacrylates, polyacrylates, polybutadienes, polyisoprenes,polyamides, polytetrahydrofurans, polyvinyl chlorides, polyacetals,amine-capped alkylene oxides, polylactides, polylactates,polypropyleneoxides, and ethylene glycol/poly(caprolactones).

The sacrificial polymers or polymeric composition is desirably readilydispersed or dissolved in common solvents, such as toluene, xylenes ormesitylene in order that the same may be coated onto a suitablesubstrate by typical coating techniques used in the industry, forexample by spin coating, spraying, meniscus, extrusion— or other coatingmethods, or by pressing, laying or otherwise adhering a preformed filmor laminated film onto the substrate.

Additional suitable sacrificial polymers for use herein includecopolymers of α-methyl styrene and vinylbenzocyclobutene, disclosed inU.S. Pat. No. 4,698,394, and polymers taught in U.S. Pat. Nos. 5,461,003and 6,165,890, and U.S. Ser. Nos. 10/445,650, 10/445,651, 10/445,652,all filed Feb. 5, 2003.

The insulating dielectric material (hardmask) may be formed from anysuitable organic polymeric material (that is a polymer comprising atleast some carbon atoms and optionally heteroatoms such as oxygen orsilicon in the backbone) or such a material that is subject to latertreatment so as to cause pore formation or to increase the permeabilitythereof to decomposition products of the sacrificial layer. A poreforming material (poragen) such as a decomposible substance or a blowingagent or a compound capable of generating a blowing agent may beincluded in the dielectric material and later activated or removed,either simultaneously with or prior to decomposition of the sacrificialmaterial, thereby introducing pores or voids in the dielectric layer, ifdesired. In one embodiment, the method is similar to that of U.S. Pat.No. 5,461,003, excepting that the porosity of the dielectric layer issubsequently induced in the step required by the present inventioneither prior to or after an optional planarization step, by any suitablelatent pore, void or cell generating technique, and the sacrificiallayer is degraded by exposure to oxygen, an oxygen plasma, or othergaseous or liquid agent. Either an open cell or closed cell structuremay be formed according to the present invention.

Suitable dielectric materials include polymeric organic substances suchas hydrocarbon polymers, functionalized organic polymers, and mixedcopolymers of carbon with silicon or boron. Preferred organic polymerichardmask substances include polyarylene homopolymers and copolymers, aswell as organic modified sesquisiloxanes, which are mixed, polymericoxides of silicon and carbon, containing both silicon, oxygen and carbonatoms in the matrix. Mixtures of the foregoing polymeric materials withaluminum oxides, aluminum silicates, or mixed aluminum/magnesiumsilicates may also be employed. All of the foregoing organic polymersmay be modified for reduction in density as disclosed herein, ifdesired.

Particularly preferred polymeric materials for use as dielectric orhardmask layers in the present invention comprise polyarylene resins,prepared by reacting polyfunctional compounds having two or morecyclopentadienone groups with polyfunctional compounds having two ormore aromatic acetylene groups. Examples of such monomers as well ascertain single component reactive monomers which contained onecyclopentadienone group together with two aromatic acetylene groups,specifically 3,4-bis(3-(phenylethynyl)phenyl)-2,5-dicyclopentadienoneand 3,4-bis(4-(phenylethynyl)phenyl)-2,5-dicyclopentadienone, andpolymers and insulative films made from such monomers were disclosed inU.S. Pat. No. 5,965,679. Typically, these materials are B-staged insolvent solution and then spin coated onto a substrate followed by ahotplate baking step and a subsequent curing (vitrification) to about400-450° C. in an oven to complete the cure. Additional examples ofsuitable polyarylene dielectric materials are disclosed in U.S. Pat.Nos. 6,359,091, 6,172,128, 6,156,812, and WO00/31183.

Additional suitable materials include organosiloxanes, preferably thecured product formed from the hydrolyzed or partially hydrolyzedreaction products of substituted alkoxysilanes or substitutedacyloxysilanes.

Hydrolysis of alkoxy or acyloxysilanes produces a mixture ofnonhydrolyzed, partially hydrolyzed, fully hydrolyzed and oligomerizedalkoxy silanes or acyloxysilanes. Oligomerization occurs when ahydrolyzed or partially hydrolyzed alkoxysilane or acyloxysilane reactswith another alkoxysilane or acyloxysilane to produce water, alcohol oracid and a Si—O—Si bond. As used herein, the term “hydrolyzedalkoxysilane” or “hydrolyzed acyloxysilane” encompasses any level ofhydrolysis, partial or full, as well as oligomerized. The substitutedalkoxy or acyloxy silane prior to hydrolysis is preferably of theformula:

wherein R is C₁-C₆ alkylidene, C₁-C₆ alkylene, arylene, or a directbond; Y is C₁-C₆ alkyl, C₂-C₆ alkenyl, a C₂₋₆alkynyl, a C₆-C₂₀ aryl,3-methacryloxy, 3-acryloxy, 3-aminoethyl-amino, 3-amino, —SiZ₂OR′, or—OR′; R′ is independently, in each occurrence, a C₁-C₆ alkyl or C₂-C₆acyl; and Z is C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂₋₆alkynyl, C₆₋₂₀ aryl, or—OR′. The term “alkylidene” refers to aliphatic hydrocarbon radicalswherein attachment occurs on the same carbon. The term “alkylene” refersto radicals, which correspond to the formula —(C_(n)H_(2n))—. The term“aryl” refers to an aromatic radical, “aromatic” being defined ascontaining (4n+2) electrons, as described in Morrison and Boyd, OrganicChemistry, 3rd Ed., 1973. The term “arylene” refers to an aryl radicalhaving two points of attachment. The term “alkyl” refers to saturatedaliphatic groups, such as methyl, ethyl, etc. “Alkenyl” refers to alkylgroups containing at least one double bond, such as ethylene, butylene,etc. “Alkynyl” refers to alkyl groups containing at least one carbon tocarbon triple bond. “Acyl” refers to a group having —C(O)R structure(for example, a C₂ acyl would be —C(O)CH₃). “Acyloxy” refers to groupshaving —OC(O)R structure. The groups previously described may alsocontain other substituents, such as halogens, alkyl groups, aryl groups,and hetero groups, such as ethers, oximino, esters, amides; or acidic orbasic moieties, that is, carboxylic, epoxy, amino, sulfonic, ormercapto, provided the alkoxysilane remains compatible with the othercomponents of the coating composition. Preferably, the silanes used aremixtures of silanes. The silanes may be alkoxy silane, acyloxy silane,trialkoxy-silanes, triacyloxysilanes, dialkoxysilanes, diacyloxysilanes,tetraalkyoxysilane or tetra-acyloxysilanes. Examples of some of theorganic groups directly attached to the silicon atom may be such thingsas phenyl, methyl, ethyl, ethacryloxypropyl, aminopropyl,3-aminoethylaminopropyl, vinyl, benzyl, bicycloheptenyl,cyclohexenylethyl, cyclohexyl, cyclopentadienylpropyl, 7-octa-1-enyl,phenethyl allyl or acetoxy. The silanes are preferably hydrolyzed orpartially hydrolyzed by a solventless process. The silanes will retainorganic portions even after cure, provided some organic groups arebonded directly to the silicon atom. In order to balance desiredproperties in the hardmask layer, a mixture of silanes may be used. Forexample, applicants have found that use of an aryl alkoxy or arylacyloxy silane (such as, phenyltrimethoxy silane) in combination with analkyloxysilane or acyloxysilane having a group with unsaturatedcarbon-=bon bonds (for example alkenyl or alkyidenyl moieties such asvinyl or phenyethynyl) provides excellent wetting, coating and adhesionproperties with sacrificial polymeric materials, and ultimately with theconductive layers to which they adhere. The presence of the aromaticsubstituted silane also improves moisture sensitivity and may improvedielectric constant over single silane systems. Furthermore, usingalkylalkoxy silanes or alkyl acyloxy silanes (such asmethyltrimethoxysilane or ethyltrimethoxysilane) in combination with thearyl and unsaturated substituted silanes has been found to furtherimprove moisture retention/exclusion and reduce dielectric constant inthe resulting hardmask. Furthermore, a mixture of monoalkoxy,monoacyloxy, dialkoxy, diacyloxy, trialkoxy, triacyloxy, tetraalkoxysilanes or tetraacyloxy silanes may be used in the mixtures as well toenable enhancement of etch selectivity, adjustment of branching, etc.

Particularly, preferred is the following composition which is thehydrolzyed or partially hydrolyzed product of a mixture comprising

-   -   (a) 50-95 mole percent silanes of the formula:        wherein Ra is C₁-C₆ alkylidene, C₁-C₆ alkylene, arylene, or a        direct bond; Ya is C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂₋₆alkynyl,        C₆-C₂₀ aryl, 3-methacryloxy, 3-acryloxy, 3-aminoethyl-amino,        3-amino, —SiZa₂ORa′, or —ORa′; Ra′ is independently, in each        occurrence, a C₁-C₆ alkyl or C₂-C₆ acyl; and Za is C₁-C₆ alkyl,        C₂-C₆ alkenyl, C₂₋₆alkynyl, C₆₋₂₀aryl, or —ORa′, provided at        least one of Za or the combination Ra-Ya comprises a        non-aromatic carbon carbon bond unsaturation,    -   (b) 5 to 40 mole percent silanes of the formula:        wherein Rb is C₁-C₆ alkylidene, C₁-C₆ alkylene, arylene, or a        direct bond; Yb is C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂₋₆alkynyl,        C₆-C₂₀ aryl, 3-methacryloxy, 3-acryloxy, 3-aminoethyl-amino,        3-amino, —SiZb₂ORb′, or —ORb′; Rb′ is independently, in each        occurrence, a C₁-C₆ alkyl or C₂-C₆ acyl; and Zb is C₁-C₆ alkyl,        C₂-C₆ alkenyl, C₂₋₆alkynyl, C₆₋₂₀aryl, or —ORb′, provided at        least one of Zb or the combination of Rb—Yb comprises an        aromatic ring, and    -   (c) 0 to 45 mole percent of silanes of the formula:        wherein Rc is C₁-C₆ alkylidene, C₁-C₆ alkylene, arylene, or a        direct bond; Yc is C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂₋₆alkynyl,        C₆-C₂₀ aryl, 3-methacryloxy, 3-acryloxy, 3-aminoethyl-amino,        3-amino, —SiZc₂ORc′, or —ORc′; Rc′ is independently, in each        occurrence, a C₁-C₆ alkyl or C₂-C₆ acyl; and Zc is C₁-C₆ alkyl,        C₂-C₆ alkenyl, C₂₋₆alkynyl, C₆₋₂₀aryl, or —ORc′, provided at        least one of Zc or the combination of Rc-Yc comprises an        alkenyl. The foregoing mole percentages are based on total moles        of silanes (a), (b) and (c) in the hardmask composition.

According to one embodiment of the invention, the material forming thehardmask layer may contain a small portion of a pore forming substancewhich decomposes after formation of the layer, thereby reducing thedensity of the dielectric material or increasing the permeabilitythereof to decomposition products of the sacrificial polymer layer.Suitable pore forming substances (poragens) include carbon particles,carbon fibers (including carbon nanotubes), crosslinked polymers, blockcopolymers, and bulky dendridic type polymers. Desirably, the poragen ispresent in the dielectric material in an amount from 1 to 50, preferablyfrom 5 to 25 percent, based on total hardmask material weight.

Suitable poragens for use in the hardmask include any compound that canform small domains in a matrix formed from the precursors and which canbe subsequently removed, for example by thermal decomposition. Preferredporagens are polymers including homopolymers and interpolymers of two ormore monomers including graft copolymers, emulsion polymers, and blockcopolymers. Suitable thermoplastic materials include polystyrenes,polyacrylates, polymethacrylates, polybutadienes, polyisoprenes,polyphenylene oxides, polypropylene oxides, polyethylene oxides,poly(dimethylsiloxanes), polytetrahydrofurans, polyethylenes,polycyclohexylethylenes, polyethyloxazolines, polyvinylpyridines,polycaprolactones, polylactic acids, copolymers of the monomers used tomake these materials, and mixtures of these materials. The thermoplasticmaterials may be linear, branched, hyperbranched, dendritic, or starlike in nature. The poragen may also be designed to react with thecross-linkable matrix precursor during or subsequent to B-staging toform blocks or pendant substitution of the polymer chain. For example,thermoplastic polymers containing reactive groups such as vinyl,acrylate, mettacrylate, allyl, vinyl ether, maleimido, styryl,acetylene, nitrile, furan, cyclopentadienone, perfluoroethylene, BCB,pyrone, propiolate, or ortho-diacetylene groups can form chemical bondswith the cross-linkable matrix precursor, and then the thermoplastic canbe removed to leave pores. The poragen added to the hardmask material isdesirably a material that results in formation of voids or pores in thematrix having an average pore diameter from 1 to 200 nm, more preferablyfrom about 2 to 100 nm, most preferably from about 5 to 50 nm. Suitableblock copolymers include those wherein one of the blocks is compatiblewith cross-linked polymer matrix resin and the other block isincompatible therewith. Useful polymer blocks can include polystyrenessuch as polystyrene and poly-α-methylstyrene, polyacrylonitriles,polyethylene oxides, polypropylene oxides, polyethylenes, polylacticacids, polysiloxanes, polycaprolactones, polyurethanes,polymethacrylates, polyacrylates, polybutadienes, polyisoprenes,polyvinyl chlorides, and polyacetals, and amine-capped alkylene oxides(commercially available as Jeffamine™ polyether amines from HuntsmanCorp.).

Preferably, the porogens employed in the hardmask composition aregrafted to a B-stageable precursor. This may be accomplished by addingthe porogens to monomers prior to B-staging as residual ethylenicallyunsaturated groups on the porogen are available to react with reactivegroups on the monomers. Alternatively, some B-staging may occur prior toaddition of the porogen and the porogen may be grafted by subjecting themixture to conditions sufficient to cause residual ethylenicallyunsaturated groups on the porogen to react with residual react groups inthe B-staged reaction product. The mixture is then coated onto asubstrate (preferably solvent coated as for example by spin coating byknown methods). The matrix is cured and the porogen is removed byheating it past its thermal decomposition temperature.

Highly preferred poragens are crosslinked polymers made by an emulsionpolymerization. Emulsion polymerization techniques are known in the art,and elaborated, for example, in numerous literature sources. Very smallcrosslinked hydrocarbon based polymer particles have been prepared in anaqueous emulsion polymerization by use of one or more anionic-,cationic-, or non-ionic surfactants. Examples of such preparations maybe found in J. Dispersion Sci. and Tech., vol. 22, No. 2-3, 231-244(2001), The Applications of Synthetic Resin Emulsions, H. Warson, ErnestBenn Ltd., 1972, p.88, and Colloid Polym. Sci., 269, 1171-1183 (1991),Polymer Bull., 43, 417-424 (1999), and U.S. Ser. No. 10/077642, filedFeb. 15, 2002 among other sources.

In another embodiment of the invention, the hardmask layer includes acell forming substance, such as a blowing agent, an azide, a volatileorganic or inorganic forming substance, or a polymer that is subject toswelling and subsequent shrinkage, thereby creating a void space withina matrix of the dielectric material. In this manner, porosity is createdin the dielectric material, the density is reduced, or the permeabilityof the dielectric material to the decomposition products of thesacrificial layer is increased.

Suitable solvents for use in preparing formulations of the hardmasklayers herein include known solvents useful in processing thermosetpolyarylene precursor compositions. The solvent may be a single solventor a mixture of one or more solvents. Examples include mesitylene,pyridine, triethylamine, N-methylpyrrolidinone (NMP), methyl benzoate,ethyl benzoate, butyl benzoate, cyclopentanone, cyclohexanone,cycloheptanone, cyclooctanone, cyclohexylpyrrolidinone, and ethers orhydroxy ethers such as dibenzylethers, diglyme, triglyme, diethyleneglycol ethyl ether, diethylene glycol methyl ether, dipropylene glycolmethyl ether, dipropylene glycol dimethyl ether, propylene glycol phenylether, propylene glycol methyl ether, tripropylene glycol methyl ether,toluene, xylene, benzene, dipropylene glycol monomethyl ether acetate,dichlorobenzene, propylene carbonate, naphthalene, diphenyl ether,butyrolactone, dimethylacetamide, dimethylformamide and mixturesthereof.

Referring now to FIGS. 1-6, wherein is shown diagrammatic cross-sectionsof a portion of a semiconductor structure, illustrating several steps ofa method according to one aspect of the instant invention. In FIGS. 1and 2 a patterned layer of a sacrificial polymer 30 is formed on asubstrate 32. The substrate 32 may be patterned or unpatterned. Thesubstrate may be a base layer or a layer of material overlaying a baselayer such as an insulating layer of silicon dioxide that may overliethe devices on an integrated circuit chip (not shown). By way ofspecific example, the substrate may be a semiconductor wafer that may,for example, contain transistors, diodes, and other semiconductorelements (as are well known in the art).

As depicted in FIG. 1, the sacrificial layer 30 is deposited on thesubstrate 32, in a relatively uniform thin layer, by spin coating, spraycoating or meniscus coating, chemical vapor deposition, plasma enhancedchemical vapor deposition, sol-gel process, or other suitable method,most preferably by spin coating a solution thereof and removing thesolvent.

In FIG. 2, the sacrificial layer is patterned to correspond to thedesired pattern of one or more air gaps to be formed in thesemiconductor device. Any suitable technique can be used to pattern thesacrificial layer, including, for example, laser ablating, etching, etc.The sacrificial layer may also be made photosensitive to facilitatepatterning.

In FIG. 3, a layer of conductive material 34, usually a metal such ascopper or aluminum is deposited in the ablated areas of sacrificiallayer 30 and over remaining portions thereof. This may be done by anysuitable technique including, for example, metal sputtering, chemicalvapor deposition (CVD), physical vapor deposition (PVD), electroplating,electroless plating, etc.

In FIG. 4, the conductive layer 34 is planarized if needed by anysuitable technique including, for example, chemical mechanical polishing(CMP). If CMP is used, an etch stop (such as a layer of silicon dioxideor other suitable material) may be applied to the surface of thesacrificial layer. The skilled artisan will realize that the order offorming the various layers can of course be reversed with a patternedconductive layer 34 being first formed on a substrate by any suitabletechnique, and the sacrificial layer 30 subsequently formed thereafterand the surface planarized to expose separate surfaces of conductivelayer 34 and sacrificial polymer layer 30. Moreover, the foregoingprocess may be repeated one or more times to create a multiple levelsemiconductor device according to the invention.

As seen in FIG. 4, the conductive layer 34 can be conveniently formedwith a height less than the height of the adjacent sacrificial material.As will be appreciated, this will result in air gaps that extend abovethe tops of the metal leads, as is desirable to reduce capacitivecoupling. The skilled artisan will also appreciate that the substrate 32could be selectively ablated or removed in a pattern corresponding tothe pattern of the sacrificial material (not depicted), so that theresultant air gaps will extend below the level of the substrate uponwhich the conductive layer is deposited.

In FIG. 5, a permanent dielectric or hardmask 36 according to theinvention is deposited over the surface of sacrificial layer 30 andconductive layer 34. The permanent dielectric 36 is deposited as a solidlayer and covers the sacrificial layer 30 and at least the exposedsurfaces of the conductive layer 34. If desired, an oxide coating may beapplied to the exposed outer surface of the conductive layer 34 or thesurface reduced to a height less than that of the adjacent sacrificiallayer to eliminate or decrease fringe effect. The permanent dielectriclayer may be planarized before or after removal of the sacrificialmaterial, if desired, as well. The permanent dielectric layer may bedeposited by spin coating, spray coating or meniscus coating, chemicalvapor deposition, plasma enhanced chemical vapor deposition, sol-gelprocess, or other method.

The material comprising the sacrificial layer 30 is removed through thepermanent dielectric layer 36 to form the air gaps 38 shown in FIG. 6.The removal of the sacrificial layer preferably is accomplished bythermal decomposition and passage of one or more of the decompositionproducts through the permanent dielectric layer 36 by diffusion.Desirably, the molecular weights of the degradation products from thesacrificial layer are relatively low, thereby facilitating their removalfrom the semiconductor structure. Highly desirably, the compounds usedas a sacrificial layer undergo thermal decomposition at temperaturesfrom 300 to 500° C., preferably from 350 to 450° C., most preferablyfrom 400 to 425° C., with essentially no residue (that is, less than 5weight percent residue) being left in the air gaps of the resultantsemiconductor structure 40.

The rate of decomposition of the sacrificial layer should be slow enoughso that diffusion through the permanent dielectric will occur withoutphysical distortion of the permanent dielectric layer. Diffusiontypically arises from a pressure build-up within the air gap. Thispressure build-up should not be so great as to exceed the mechanicalstrength of the permanent dielectric. Increased temperature willgenerally aid diffusion as diffusivity of gas through the permanentdielectric will normally increase with temperature.

As will be appreciated, the air gaps may contain residual gas from thedecomposition although generally such residual gas will eventuallyexchange with air. Steps may be taken to prevent such exchange, or todispose a different gas (a noble gas for example) and/or a partialvacuum in the air gaps. For example, the semiconductor structure may besubjected to vacuum conditions to extract any residual gas from the airgaps by diffusion or otherwise after which the semiconductor structuremay be coated by a suitable sealing material. Before the semiconductorstructure is sealed, it may be subjected to a controlled gas atmosphere,such as one containing a noble gas, to fill the air gaps with such gas.Further processing steps may be performed on the semiconductor structure40, for example to form additional layer(s) of interconnection in thesemiconductor device having air gaps above and below conductor lines aswell as air gaps on the sides of conductor lines. Thus, the sacrificiallayer of the instant invention may be decomposed as a single layerbefore each next interconnect level or multiple layers of sacrificialmaterial may be simultaneously decomposed after multiple interconnectlevels have been built. Preferably, the entire multiple layerinterconnect structure is built and the layers decomposedsimultaneously. Those skilled in the art will also appreciate that manytechniques may be employed to remove or decompose the sacrificial layer.However, thermal decomposition is the preferred technique.

If desired one or more impermeable coating or encapsulating layers(sealing layers) (not depicted) may be applied over the hardmask toprevent further gas exchange with the semiconductor structure. Themethod of the instant invention is not limited to the specific stepsoutlined above with reference to FIGS. 1-6. For example, U.S. Pat. Nos.6,165,890 and 5,965,679, and numerous other references disclose othersuitable techniques and structures.

The following examples are for illustrative purposes only and are notintended to limit the scope of this invention. Densities are measured byRutherford Back Scattering (RBS).

EXAMPLE 1

A) Sacrificial Polymer-α-methyl styrene/vinylbenzocyclobutene copolymer

A one liter round bottom flask is equipped with a magnetic stirring bar,a thermometer, a gas inlet adapter and a septum. The flask is heated to110 degrees Celsius and dried with a stream of dry nitrogen. The flaskis then cooled in an ice/water bath. 400 milliliters of dry cyclohexaneand 38 milliliters of dry tetrahydrofuran are added to the flask. 82.6grams of alpha methyl styrene (passed over alumina to remove inhibitorand then distilled from calcium hydride) is added to the flask bycannula. 39 grams of vinylbenzocyclobutene (purified by distillationfrom calcium hydride, treated with butyl lithium to a persistent colorand then distilled again) is added to the flask by syringe.

The temperature of the flask is brought to 8 degrees Celsius. 4.6milliliters of 0.725 molar sec butyl lithium solution in cyclohexane isadded to the flask with stirring to initiate polymerization. Thetemperature of the flask rises to 12 degrees Celsius. The flask isstirred for two hours. 2 milliliters of isopropanol is then added to theflask. The polymer produced in the flask is precipitated by adding moreisopropanol, dried, dissolved in methylene chloride, precipitated inmethanol and then dried.

The dried polymer weighs 82 grams. Proton NMR analysis indicates thatthe dried polymer is a copolymer of alpha methyl styrene andvinylbenzocyclobutene. Proton NMR analysis also indicates that the driedpolymer is 29.7 weight percent vinylbenzocyclobutene. Gel PermeationChromatography analysis indicates that the number average molecularweight of the dried polymer is 16,300 grams per mole compared topolystyrene standards with a polydispersity of 1.11. DifferentialScanning Calorimitery shows a glass transition temperature of 200degrees Celsius prior to benzocyclobutene cure, then a glass transitiontemperature of 350 degrees Celsius after curing at 280 degrees Celsius(the cyclobutene group on the polymer opens at 280 degrees Celsius andcross-links the polymer by way of reaction with a neighboringcyclobutene group, see Kirchhoff et al., Prog. Polym. Sci. Vol 18,85-185, 1993, the cyclobutene rings on the benzocyclobutene moietiesbegin to undergo ring opening at a significant rate at 200 degreesCelsius with a polymerization exotherm maximum temperature at 250-280degrees Celsius). Six grams of the dried polymer (uncured) is dissolvedin fourteen grams of mesitylene and filtered with a one micron pore sizefilter. Two milliliters of the filtered polymer solution is spin coated(3,500 rpm) on a semiconductor substrate to produce a sacrificial layerof a semiconductor device.

B) Dielectric Polymer Formation

a) (4-(3,5-bis(Phenylethynyl)phenyl)2,3,5-triphenylcyclopentadienone)Synthesis of 1-Phenylethynyl-3,5-Dibromobenzene

1,3,5-Tribromobenzene (31.48 grams, 0.10 mole); phenylacetylene (10.22grams, 0.10 mole); anhydrous, nitrogen sparged triethylamine (48.18grams, 0.476 mole); triphenylphosphine (0.66 gram, 0.00253 mole);palladium (II) acetate (0.09 gram, 0.00041 mole) and anhydrous, nitrogensparged N,N-dimethylformamide (90 milliliters) were added under a drynitrogen atmosphere to a predried 500 milliliter glass three neck roundbottom reactor containing a predried magnetic stirring bar. The reactorwas additionally outfitted with a fan cooled spiral condenser and athermometer with thermostatically controlled heating mantle. Stirringand heating commenced, and after 14 minutes, when a temperature of 35°C. was achieved, a clear, light amber colored solution formed. After acumulative 1.6 hours reaction time, a temperature of 80° C. was achievedand maintained for the next 17.2 hours. At this time, high pressureliquid chromatographic (HPLC) analysis indicated that full conversion ofthe phenylacetylene reactant had been achieved. The reactor contentswere poured over cracked ice contained in a 2 liter beaker. Aftercomplete melting of the ice, the precipitated product was recovered viafiltration through a medium fritted glass funnel. The product cake onthe funnel was washed with two portions (100 milliliter) of deionizedwater, then directly recrystallized, as a damp product, from boilingethanol (350 milliliters total volume at boiling). The recrystallizationsolution was allowed to cool to room temperature and held there for 16hours to provide 17.1 grams of a light yellow fibrous crystallineproduct after recovery via filtration and drying under vacuum (40° C.and 1 mm Hg). HPLC analysis revealed the presence of the desired1-phenylethynyl-3,5-dibromobenzene product at 89 area percent, residual1,3,5-tribromobenzene at 4 area percent and the 7 area perccent balanceas a single unknown. The spectrum as determined by ¹H nuclear magneticresonance (NMR) analysis was consistent with the desired product.

Synthesis of 3,5-Dibromobenzil

A portion of the product containing 1-phenylethynyl-3,5-dibromobenzene(6.94 grams) and dimethylsulfoxide (100 milliliters) were added to a 500milliliter glass three neck round bottom reactor outfitted with achilled (2° C.) condenser, a thermometer with thermostaticallycontrolled heating mantle, and a magnetic stirring bar. The reactorcontents were heated as a stirred solution to 140° C., then iodine (0.07gram, 0.00055 mole) was added. After 3 days at the 140° C. reactiontemperature, the hot product solution was cooled to 25° C., resulting inthe formation of a yellow crystalline slurry. The slurry was added to abeaker containing a stirred mixture of 10 percent aqueous sodiumhydrosulfite (87 milliliters), deionized water (100 milliliters) anddiethyl ether (200 milliliters). After stirring for one hour, thediethyl ether layer was recovered in a separatory funnel, then washedwith three portions (75 milliliter) of deionized water. The recovereddiethyl ether solution was dried over anhydrous sodium sulfate andfiltered through a medium fritted glass funnel to provide a filtratewhich was then rotary evaporated to dryness. The crude product wasrecrystallized from boiling ethanol. The recrystallization solution wasallowed to cool to room temperature and held therein for 16 hours toprovide 5.70 grams of a light yellow fluffy crystalline product. HPLCanalysis revealed the presence of the desired 3,5-dibromobenzil productat 99 area percent with the 1 area percent balance as a single unknown.The ¹H NMR spectrum corresponded to that of the desired product.

Synthesis of 3,5-bis(Phenylethynyl)benzil

3,5-Dibromobenzil (12.50 grams, 0.0679 bromine equivalent);phenylacetylene (8.40 grams, 0.0822 mole); anhydrous, nitrogen spargedtriethylamine (18.77 grams, 0.186 mole); triphenylphosphine (0.45 gram,0.0017 mole); palladium (II) acetate (0.06 gram, 0.00028 mole) andanhydrous, nitrogen sparged N,N-dimethylformnamide (79 milliliters) wereadded under a dry nitrogen atmosphere to a predried 500 milliliter glassthree neck round bottom reactor containing a predried magnetic stirringbar. The reactor was additionally outfitted with a fan cooled spiralcondenser and a thermometer with a thermostatically controlled heatingmantle. Stirring and heating of the light amber colored solution wascommenced and after 13 minutes, a temperature of 80° C. was achieved andmaintained for the next 15.1 hours. At this time, HPLC analysisindicated that full conversion of the 3,5-dibromobenzil reactant hadbeen achieved. The reactor contents were poured over cracked icecontained in a 2 liter beaker. After complete melting of the ice, theprecipitated product was recovered via filtration through a mediumfritted glass funnel. The product cake on the funnel was washed with twoportions (100 milliliter) of deionized water, then directlyrecrystallized, as a damp product, from boiling acetone (160 milliliterstotal volume at boiling). The recrystallization solution was allowed tocool to room temperature and held therein for 16 hours to provide 10.90grams (78.2 percent isolated yield) of a yellow fibrous crystallineproduct after recovery via filtration and drying under vacuum (40° C.and 1 mm Hg). HPLC analysis revealed the presence of the desired3,5-bis(phenylethynyl)benzil product at 100 area percent. The ¹H NMRspectrum was consistent with the desired product. The product identitywas confirmed by electron ionization mass spectroscopic analysis (EIMS).

Synthesis of4-(3,5-bis(Phenylethynyl)phenyl)-2,3,5-triphenylcyclopentadienone

A portion of the 3,5-bis(phenylethynyl)benzil (10.87 grams, 0.0265mole), 1,3-diphenylacetone (5.90 grams, 0.0281 mole), anhydrous1-propanol (300 milliliters) and anhydrous toluene (17 milliliters),both of which had been sparged with dry nitrogen, were added under a drynitrogen atmosphere to a predried 500 milliliter glass three neck roundbottom reactor containing a predried magnetic stirring bar. The reactorwas additionally outfitted with a fan cooled spiral condenser and athermometer with thermostatically controlled heating mantle. Stirringand heating commenced, and once a refluxing clear light yellow coloredsolution formed, benzyltrimethylammonium hydroxide (40 percent inmethanol) (0.91 gram) was added, immediately inducing a dark red color.After maintaining the reflux for 20 minutes, HPLC analysis indicatedthat full conversion of the 3,5-bis[phenylethynyl)benzil reactant hadbeen achieved. After a cumulative 30 minutes of reaction, the heatingmantle was removed from the reactor, and the stirred contents weremaintained at 24° C. for the next 16 hours. The product was recoveredvia filtration through a medium flitted glass funnel. The product cakeon the funnel was washed with two portions (50 milliliters) of1-propanol, then dried in a vacuum oven to provide 11.84 grams (76.4percent isolated yield) of4-(3,5-bis(phenylethynyl)phenyl)-2,3,5-triphenylcyclopentadienone(unsymmetrically substituted 3,5-AAB monomer) as a dark red purplecolored crystalline product. HPLC analysis revealed the presence of thedesired product at 100 area percent. The product's identity wasconfirmed by ¹H NMR and EI MS analysis.

Spin Coating Dielectric (Hardmask) Material

Spin coating compositions of4-(3,5-bis(Phenylethynyl)phenyl)-2,3,5-triphenylcyclopentadienone withand with out crosslinked styrene/divinylbenzene microemulsionpolymerized particles at 20 percent loading level and γ-butyrolactonediluent were B-staged by heating to 200° C. for 48 hours. The poreforming materials were prepared by the technique of microemulsionpolymerization at 30° C., using high purity deionized water; anonylphenol ethoxylate surfactant such as Tergitol™ NP-15, availablefrom The Dow Chemical Company; a 90/10 (w/w) styrene/divinylbenzenemonomer mix; and a free radical initiator comprisingt-butylhydroperoxide and ascorbic acid to give very small, <50 nm Dv,poragen particles. The resultant solutions were diluted withcyclohexanone to give 20 percent solids solutions. These solutions maythen be used to prepare spun coated, cured dielectric coatings havingdensities of 1.05 g/cm³. In the case of the poragen containing hardmaskmaterial, the poragen was removed by thermal degradation to furtherreduce the density of the coating to 0.9 g/cm³.

By combining the foregoing sacrificial polymer layers and dielectricpolymer layers on a semiconductor substrate to produce a system likethat shown in FIG. 1 which is then processed as shown in FIGS. 2-6, asemiconductor device having air gaps is produced.

EXAMPLE 2

A 5 percent mesitylene solution of a styrene/vinylbenzocyclobutenecopolymer containing 70 mole percent polymerized styrene and 30 molepercent polymerized vinylbenzocyclobutene is prepared for use as thesacrificial polymer.

A cross-linkable organosiloxane composition for use as an oligomericprecursor for the hardmask is prepared by hydrolysis and subsequentcopolymerization of vinyl triacetoxysilane and phenyl trimethoxysilanemonomers as described in WO 02/16477.

A multilayer electronic device is prepared in the following manner:

-   -   1) The sacrificial polymer solution described above is dispensed        onto an electronic substrate at 60 rpm, spun at 3000 rpm for 30        seconds and baked at 250° C. for 20 minutes under nitrogen.    -   2) The sacrificial polymer coating is patterned using standard        lithographic and etching methods to form an interconnection        pattern. Conductive metal is deposited into the interconnection        pattern. The surface of the wafer is polished via        chemical/mechanical polishing to remove deposited metal        overburden and provide a level surface of exposed conductors and        sacrificial polymer.    -   3) The cross-linkable organosiloxane solution described above is        diluted to 4 percent solids in propylene glycol methylether        acetate (Dowanol™ PMA, available from The Dow Chemical Company).        This solution is applied at 600 rpm to the surface of the wafer,        spun at 3000 rpm for 30 seconds, and baked 265° C. for 60        seconds; thus creating a hardmask dielectric layer having a        density of 1.3 g/cm³.    -   4) The sample multilayer wafer is placed in an oven under        nitrogen at room temperature, ramped to 430° C. over one hour,        and held at 430° C. for 40 minutes. After cooling to room        temperature, the hardmask layer is found to be free of defects        by optical inspection. Microscopic examination reveals that the        sacrificial polymer is removed by degradation and subsequent        permeation through the hardmask, without detrimental effect on        the hardmask layer.

The above process steps, or at least steps 1)-3), may be repeated foradditional layers of interconnect, optionally with deposition of aninterposed layer of a dielectric or substrate material. The removal ofthe sacrificial polymer layer or layers, described in step 4, may beconducted after each repeat of step 3) or once after multipleinterconnected layers of the semiconductor device have been formed.

1. A method of forming at least a partial air gap within asemiconducting device comprising the steps of: (a) depositing asacrificial polymeric composition in one or more layers of the deviceduring its formation; (b) coating the device with one or more layers ofa relatively non-porous, organic, polymeric, insulating dielectricmaterial (hardmask) having a density less than 2.2 g/cm³; and (c)decomposing the sacrificial polymeric composition such that thedecomposition products permeate at least partially through the one ormore hardmask layers, thereby forming at least a partial air gap withinthe device.
 2. The method of claim 1, wherein the sacrificial polymer isa copolymer of a first monomer selected from the group consisting ofacrylates, vinylaromatics, norbomenes, and alkyldiol diacrylates with asecond monomer selected from the group consisting ofvinylbenzocyclobutenes and 1,3 bis2[4-benzocyclobutenyl(ethenyl)]benzene.
 3. The method of claim 1,wherein the sacrificial polymer is a copolymer of (a)5-ethylidene-2-norbornene and vinylbenzocyclobutene (or avinylbenzocyclobutene derivative); (b) 5-ethylidene-2-norbomene and5-(3-benzocyclobutylidene)-2-norbornene; (c) styrene (or a styrenederivative) and 5-(3-benzocyclobutylidene)-2-norbornene; (d) styrene (ora derivative of styrene) and vinylbenzocyclobutene (or avinylbenzocyclobutene derivative); or (e)bis[3-(4-benzocyclobutenyl)]1,n (n=2-12)alkyldiol diacrylate and 1,3 bis2[4-benzocyclobutenyl(ethenyl)]benzene.
 4. The method of claim 1,wherein the sacrificial polymer is a copolymer comprising from 99 to 40mole percent styrene or a styrene derivative and from 1 to 60 molepercent vinylbenzocyclobutene or a vinylbenzocyclobutene derivativebased on total moles of incorporated monomers in the polymer.
 5. Themethod of claim 1, wherein the sacrificial polymer is a copolymer ofα-methylstyrene and vinylbenzocyclobutene.
 6. The method of claim 1wherein the hard mask is the cured product formed from the hydrolyzed orpartially hydrolyzed reaction products of substituted alkoxysilanes orsubstituted acyloxysilanes.
 7. The method of claim 6 wherein the hardmask comprises the hydrolyzed reaction product of a substituted alkoxyor acyloxy silane of the formula:

wherein R is C₁-C₆ alkylidene, C₁-C₆ alkylene, arylene, or a directbond; Y is C₁-C₆ alkyl, C₂-C₆ alkenyl, a C₂₋₆alkynyl, a C₆-C₂₀ aryl,3-methacryloxy, 3-acryloxy, 3-aminoethyl-amino, 3-amino, —SiZ₂OR′, or—OR′; R′ is independently, in each occurrence, a C₁-C₆ alkyl or C₂-C₆acyl; and Z is C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂₋₆alkynyl, C₆₋₂₀aryl, or—OR′.
 8. The method of claim 1 wherein the dielectric material comprisesa polyarylene resin.
 9. The method of any of claims 1-8 wherein thedielectric material comprises a pore forming substance that is activatedor removed, either simultaneously with or prior to decomposition of thesacrificial material, thereby introducing pores or voids in the layer.10. The method of claim 9 wherein the pore forming substance is acrosslinked emulsion polymerized copolymer.
 11. A semiconducting devicecomprising an air gap prepared by a method according to any one ofclaims 1-8.
 12. A semiconducting device comprising an air gap preparedby a method according to claim
 9. 13. A semiconductor device comprisinga substrate layer, one or more conductive layers, at least one layer ofa relatively non-porous, organic polymeric insulating dielectricmaterial having a density less than 2.2 g/cm³, and optionally animpermeable organic or inorganic sealing layer, wherein at least someportion of the conductive layer is separated from another portionthereof by at least a partial air gap.